The present invention relates to plasma CVD method and apparatus for forming a film on a substrate to be deposited, i.e., a deposition target object by forming a plasma from a deposition material gas and by exposing the object to the plasma.
A plasma CVD method has been widely used for manufacturing various kinds of semiconductor devices such as ICs and sensors utilizing semiconductors, manufacturing various kinds of thin-film devices used in solar cells and LCDs (liquid crystal displays), forming films having a high wear resistance on mechanical parts and tools requiring a high wear resistance, and others. Various apparatuses for implementing the plasma CVD method have been known, and a plasma CVD apparatus of a capacity coupling type shown in FIG. 8 is an example of such an apparatus.
The apparatus shown in FIG. 8 is known as a parallel-plated plasma CVD apparatus, and has a vacuum container 1 used as a deposition chamber, in which an electrode 2 also serving as an object holder for carrying a substrate S, i.e., a deposition target object S as well as an electrode 3 opposed to the electrode 2 are arranged.
The electrode 2 is usually used as a ground electrode, and is additionally provided with a heater 21 for heating the object S mounted thereon to a deposition temperature. When the object S is heated by a radiation heat, the heater 21 is separated from the electrode 2.
The electrode 3 is an electric power applying electrode for applying an electric power to a deposition material gas, which is introduced between the electrodes 2 and 3, for forming a plasma. In the illustrated example, the electrode 3 is connected to an RF (radio-frequency) power source 32 via a matching box 31.
The vacuum container 1 is connected via piping to an exhaust device 5, and is also connected via a piping to a gas supply unit 4 of the deposition material gas. The gas supply unit 4 includes one or more gas sources 431, 432, . . . for supplying deposition material gases connected to mass flow controllers 411, 412, . . . and valves 421, 422, . . . .
According to this parallel-plated plasma CVD apparatus, the deposition target object S is transported into the vacuum container 1 by an unillustrated object transporting device, and is mounted on the electrode 2. The exhaust device 5 operates to achieve a predetermined degree of vacuum in the container 1, and the gas supply unit 4 supplies the deposition material gas into the container 1. The RF electrode 3 is supplied with an RF power from the power source 32, and thereby the plasma is produced from the introduced gas. A film is deposited on the surface of the object S in the plasma thus produced.
A plasma CVD apparatus of an induction coupling type shown in FIG. 9 has also been used. This apparatus differs from the apparatus in FIG. 8 in that the object holder 2 is electrically floated, the electrode 3 in FIG. 8 is replaced with an induction coil electrode 7 wound around the container 1, and the matching box 31 and the RF power source 32 are connected to the opposite ends of the induction coil 7. Structures other than the above are the same as those of the apparatus in FIG. 8, and the same or similar parts and portions bear the same reference numbers.
A plasma CVD apparatus shown in FIG. 10 has also been used for forming high adherence films for engineering purposes and other films. The apparatus in FIG. 10 differs from the apparatus in FIG. 8 in that the electrode 2 also serving as the object holder is used as the power applying electrode for applying the electric power, and the electrode 3 opposed to the electrode 2 is used as the ground electrode. In the illustrated example, the electrode 2 is connected to the RF power source 32 via the matching box 31. Structures other than the above are the same as those of the apparatus in FIG. 8, and the same or similar parts and portions bear the same reference numbers.
In this apparatus, ionized particles in the plasma apply an impact against the object S carried by the power applying electrode 2. Therefore, this apparatus can be suitably used for manufacturing tools, machine parts and others. In the apparatus shown in FIG. 8, ionized particles apply a less impact against the object S, so that the deposition target object S can be selected from a wider range.
In the apparatus in FIG. 10, a self-bias voltage appears on the RF electrode 2, and affects the quality of the deposited film. Generally, the deposition under the conditions of such a large self-bias voltage can achieve effects such as improvement of a deposition rate and improvement of a film hardness, although the latter depends on a kind of the film.
A plasma CVD apparatus shown in FIG. 11 is also available. This apparatus differs from the apparatus in FIG. 8 in that an RF power generating device 33 is employed instead of the RF power source 32, and is connected to the electrode 3 via the matching box 31. The RF power generating device 33 includes an RF power amplifier 34 and an RF arbitrary waveform generating device 35 connected thereto. Structures other than the above are the same as those of the apparatus in FIG. 8, and the same or similar parts and portions bear the same reference numbers.
According to this apparatus, formation of the plasma from the deposition material gas is performed by applying an RF power, on which pulse modulation or another modulation is effected, from the RF power generating device 33 to the electrode 3.
Although not shown, such plasma CVD apparatuses are also known that differ from the parallel-plated plasma CVD apparatuses in FIGS. 8 and 10, respectively, in that the matching box 31 and the RF power source 32 in FIGS. 8 and 10 are replaced with a DC power source capable of turning on/off a current. According to these apparatuses, formation of the plasma from the deposition material gas is performed by applying the DC power in a pulse form.
Although not shown, such a method has already been known that forms a plasma from the deposition material gas by applying a modulated RF power by using the induction coupling type-plasma CVD apparatus in FIG. 9 provided with RF power generating device 33 shown in FIG. 11 instead of the RF power source 32.
Various kinds of films can be formed by the plasma CVD apparatuses in the prior art already described. For example, the pressure in the vacuum container 1 is set to about several hundreds of millitorrs, and the deposition material gas supply unit 4 supplies a carbon compound gas such as a methane (CH4) gas or an ethane (C2H6) gas, or a mixture of such a carbon compound gas and a hydrogen (H2) gas, whereby a carbon (C) film is formed on the deposition target object S.
In this case, the film quality can be controlled by changing the processing temperature of the deposition target object S. For depositing a film on an object made of, e.g., a synthetic resin such as polyimide, the deposition temperature is set to about 100xc2x0 C. or less in view of the heat resistance of the object, in which case a diamond-like carbon (DLC) film is deposited. Since this DLC film has a large hardness, it is utilized as diaphragms of loud speakers and coatings of ornaments.
With increase in deposition target object temperature, the carbon film has a larger hardness. Therefore, in the case where carbon films are used as coatings for improving, e.g., a surface hardness of cutting tools, various kinds of machine parts or the like, the deposition temperature is generally set to 500xc2x0 C. or more. If the deposition temperature is set to 900xc2x0 C. or more, a diamond film is deposited.
As already described, however, the plasma CVD methods and apparatuses, which produce the plasma from the material gas by applying thereto the steady or modulated RF power or by applying the steady or pulse-form DC. power, cannot perform the film deposition at a sufficiently low temperature, and the deposited film cannot have a sufficiently large adherence to the object.
Particularly, in the case where a hard carbon film such as a DLC. film is formed by the plasma CVD method and apparatus, an internal stress is liable to occur in such a hard film due to expansion and contraction of the film itself or the like, and therefore an adjustment with respect to the surface to be deposited may be deteriorated, which tends to cause partial separation or peeling. In order to improve the film adherence, the deposition may be performed under the condition that the self-bias is large. However, this further increases the hardness of the deposited film, which reduces the film adherence.
Accordingly, a first object of the present invention is to provide plasma CVD method and apparatus for depositing a film on a deposition target substrate, i.e., deposition target object in a plasma produced by applying an electric power to a deposition material gas, and particularly plasma CVD method and apparatus which can form a film having a good adherence to the object.
A second object of the present invention is to provide plasma CVD method and apparatus for depositing a film on a deposition target substrate, i.e., deposition target object in a plasma produced by applying an electric power to a deposition material gas, and particularly plasma CVD method and apparatus which can perform film deposition at a lower temperature than the method and apparatus in the prior art.
A third object of the present invention is to provide plasma CVD method and apparatus for depositing a film on a deposition target substrate, i.e., deposition target object in a plasma produced by applying an electric power to a deposition material gas, and particularly plasma CVD method and apparatus which can form a carbon film having a high hardness and a good adherence to the object.
For achieving the first object, the present invention provides a plasma CVD method for forming a plasma from a deposition material gas by applying an electric power, and forming a film on a deposition target object, i.e., deposition target substrate in the plasma, wherein the formation of the plasma from said material gas is performed by applying an RF power and a DC. power, and the DC. power is applied to an electrode carrying the deposition target object.
For achieving the first object, the invention provides a plasma CVD apparatus for forming a plasma from a deposition material gas supplied from a deposition material gas supply unit by applying an electric power from power applying means, and exposing a deposition target substrate, i.e., a deposition target object to the plasma for forming a film on the object, wherein said power applying means includes RF power applying means and DC. power applying means, and said DC power applying means applies the power to an electrode carrying the deposition target object.
According to the plasma CVD method and apparatus of the invention, the plasma is formed from the deposition material gas while applying the DC. power to the electrode carrying the deposition target object, so that ionized particles in the plasma are accelerated toward the deposition target object, and the accelerated particles produces a cleaning effect to remove contaminants or the like sticking to the surface of the object while the deposition is being performed. In addition to this cleaning effect, ionized particles contributing to the deposition are implanted into a surface portion of the object to form a inclination composition layer, so that a film having a good adherence to the object can be formed.
According to the method and apparatus of the invention, since the ionized particles applies an impact on the deposition target object, the method and apparatus of the invention which can be used for manufacturing devices such as ICs can be used more suitably in manufacturing of tools and machine parts.
The other electrode opposed to the electrode carrying the deposition target object may be disposed in a container for deposition, and therefore may be an electrode corresponding to the electrode 3 opposed to the electrode 2 serving as the object holder in the parallel-plated plasma CVD apparatus shown in FIGS. 8, 10 and 11. Alternatively, the other electrode may be an induction coil electrode wound around the container, and therefore may be an electrode corresponding to the coil electrode 7 in the induction coupling type plasma CVD apparatus shown in FIG. 9.
In the method and apparatus of the invention, said RF power may be a modulated RF power. The modulation may be pulse modulation performed by on/off of power application or pulse-like modulation , and may be broadly an amplitude modulation.
A plasma of a high density can be produced owing to this modulation, which is effected on the RF power for plasma production from the deposition material gas, so that a reactivity is improved, and therefore deposition at a low temperature is allowed. Owing to the above modulation, the temperature of electrons and ions in the plasma is controlled to increase relatively the amount of produced radicals in the plasma which contribute to the deposition. This promotes reaction at the surface of the deposition target object, and therefore improves the film adherence and deposition rate. According to the method and apparatus of the invention, the foregoing second object can be achieved by employing the modulated RF power as the foregoing RF power.
According to the method and apparatus of the invention, a basic RF power before modulation may have, for example, a sinusoidal, square, saw-tooth-like or triangular waveform.
The basic RF power before modulation may have a predetermined frequency (e.g., 13.56 MHz) between about 10 MHz and about 100 MHZ, and a pulse modulation is effected on the basic RF power with a modulation frequency between about 1/105 and about 1/10 of the predetermined frequency, and more preferably between about 1/104 and about 1/103. In other words, the pulse-modulated RF power may be produced by affecting the pulse modulation on the basic RF power having the frequency in the above range with the modulation frequency between about 100 Hz and about 10 MHZ, and more preferably between about 1 kHz and about 100 kHz.
For deposition of a carbon (C) film which will be described later, the pulse modulation may be effected on the basic RF power of a frequency of, e.g., 13.56 MHz with the modulation frequency from about 100 Hz to about 500 kHz. In particular, for forming highly crosslinked carbon film, the modulation frequency from about 100 Hz to about 5 kHz is desirably employed. For depositing a high-density carbon film, the modulation frequency from about 10 kHz to about 100 kHz is desirably employed.
The reason for employing the basic RF power of the frequency in the above range is as follows. If it were lower than 10 MHz, the plasma density would be insufficient. Even if it were higher than 100 MHZ, the plasma density would not be improved further, and an electric power cost would uselessly increase. The reason for employing the pulse modulation frequency in the above range is as follows. If it were lower than 100 Hz, the modulation would not provide an effect of improving the plasma density. Even if it were higher than 10 MHz, the plasma density would not be improved further, and an electric power cost would uselessly increase.
The duty ratio (on-time/(on-time+off-time)) of the pulse modulation may be from about 10% to about 90%. Although not restricted, it may be typically about 50%. If it were lower than 10%, the reaction time would be short and therefore the deposition rate would lower. If it were higher than 90%, a time for power application would be excessively long, and therefore an effect of improving the plasma density by the modulated RF power would be reduced.
In the method and apparatus of the invention, the DC potential applied to the electrode carrying the deposition target object is usually negative potential. The negative potential during deposition have a magnitude, which does not cause or substantially cause etching of the deposition target object and/or the film formed thereon by ionized particles which are accelerated.
According to the method and apparatus of the invention, the RF power may be applied to the electrode carrying the deposition target object, in which case an RF power and a DC. power are applied together in a superposed manner. Alternatively, the RF power may be applied to the electrode opposed to the electrode carrying deposition target object.
In the case where the RF power is applied to the electrode carrying the deposition target object, ionized particles exert a large impact to the deposition target object. Therefore, the electrode supplied with the RF power may be selected depending on a material, purpose and others of the deposition target object.
According to the method and apparatus of the invention, the DC. power may be in a pulse form, which further improves a density of the plasma produced by electric discharging. Also, the effect of accelerating the ionized particles in the plasma toward the deposition target object may be the same or improved, because the ionized particles are particularly strongly accelerated during turn-on of the DC. power.
The frequency of the pulse modulation may be in a range from about 1 kHz to about 100 kHz, because the frequency lower than 1 kHz would not improve the effect of improving the plasma density, and the frequency higher than 100 kHz would uselessly increase the cost without further improving the effect of improving the plasma density. The duty ratio may be in a range from about 10% to about 90%, and is typically about 50%, although not restricted thereto.
In the method for forming the plasma from the deposition material gas by applying the electric power, and forming the film on the deposition target object under the plasma, an interface layer may be formed on the object, and thereafter an upper layer of the same material as the interface layer may be formed, in which case formation of the interface layer is performed by the foregoing method of the invention, and the interface layer thus formed can have a good adherence to the deposition target object.
The power applied for formation of the upper layer is not restricted, and the interface and upper layers are made of the same material and thus have good adjustment properties, so that a good adherence can be achieved between them. In addition to the interface layer, the upper layer may also be formed by the foregoing method of the invention, in which case the adherence between them can be further improved.
The method and apparatus of the invention described above may be provided with a deposition material gas supply un it which can supply, as the deposition material gas, a gas of carbon compound for forming a carbon film, or can supply a gas of a carbon compound together with a gas of a kind different from the carbon compound gas for forming the carbon film. By using such deposition material gas, the carbon film, and typically a DLC. film may be formed on the deposition target object.
In this case, since the plasma is formed from the deposition material gas while applying the DC. power to the electrode carrying the deposition target object, a carbon film having a large hardness and a good adherence may be formed on the object for the same reason as the above. Thus, this can achieve the third object of the invention.
Carbon compound for the carbon film deposition may be one or more material selected from a group including methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), acetylene (C2H2), benzene (C6H6), carbon tetrachloride (CF4) and carbon hexafluoride (C2F6) which have been generally used for carbon film deposition. Each of these materials may be solely used, or may be used together with another kind of gas such as a hydrogen (H2) gas or an inert gas for the carbon film deposition.
For forming the carbon film by the method and apparatus of the invention, there may be employed a deposition material gas supply unit which can supply, in addition to the deposition material gas for the carbon film deposition, either or both of a nitrogen (N2) gas or an ammonia (NH3) gas, whereby either or both the nitrogen gas and the ammonia gas may be supplied together with or instead of the deposition material gas for carbon film deposition before completion of the deposition (typically, immediately before completion of the deposition) while continuing application of the power, so that a carbon nitride layer may be formed at the surface portion of the carbon film.
In the case where a different kind of gas such as a hydrogen gas is used as the deposition material gas for carbon film deposition, the gas containing nitrogen (N) may be supplied instead of the deposition material gas, in which case only supply of the carbon compound gas may be stopped, and the different kind of gas may be continuously supplied, which is allowed depending on the kind of the gas.
Since the carbon nitride has an extremely high hardness, the deposited carbon film can have an improved hardness. Since both the nitride layer and the carbon film under the same contains carbon, they have good adjustment properties and therefore a good adherence.
The material of the deposition target substrate, i.e., deposition target object, on which the carbon film is deposited according to the method and apparatus of the invention, is not restricted, but may be an organic material. The organic material may be thermosetting resin, thermoplastic resin, rubber, paper, wood or the like. In the case where a hard carbon film is deposited on the object made of such a material, the conventional plasma CVD method cannot provide a sufficiently good film adherence, and partial peeling may occur. However, a sufficiently good film adherence can be obtained according to the method and apparatus of the invention.
The thermosetting resin may be phenol-formaldehyde resin, urea resin, melamine-formaldehyde resin, epoxy resin, furan resin, xylene resin, unsaturated polyester resin, silicone resin, diallyl phthalate resin or the like.
The thermoplastic resin may be vinyl resin (polyvinyl chloride, polyvinyl dichloride, polyvinyl butyrate, polyvinyl alcohol, polyvinyl acetate, polyvinyl formal or the like), polyvinylidene chloride, chlorinated polyether, polyester resin (polystyrene, styrene acrylonitrile copolymer or the like), ABS, polyethylene, polypropylene, polyacetal, acrylic resin (poly methyl methacrylate, denatured acrylic or the like), polyamide resin (nylon 6, 66, 610, 11 or the like), cellulosic resin (ethyl cellulose, acetyl cellulose, propyl cellulose, cellulose acetate butyrate, cellulose nitrate or the like), polycarbonate, phenoxy resin, fluorocarbon resin (trifluoro chloro ethane, ethylene tetrachloride, ethylene tetrachloride propylene hexafluoride, vinylidene fluoride or the like), or polyurethane or the like.
The rubber may be natural rubber, butyl rubber, ethylene-propylene rubber, chloroprene rubber, chlorinated polyethylene rubber, epichlorohydrin rubber, acrylic rubber, nitrile rubber, urethane rubber, silicone rubber, fluororubber or the like.
The thermosetting resin may be used as a material of films, phonograph records, various kinds of nets, buttons, ornaments, toys, stationery, and sporting goods, and may also be used as a material of household articles such as kitchenwares, various kinds of containers, tableware. It may further be used as a material of electric parts such as insulators or terminals, or machine parts such as fuel tanks, automobile bodies, automobile bumpers or bearings.
The thermoplastic resin may be used as a material of films, phonograph records, various kinds of nets, buttons, ornaments, toys, stationery, sporting goods, and may be used as a material of household articles such as kitchenwares, various kinds of containers or tableware. It may further be used as a construction material, e.g., for water pipings, building members or floor members, or a material of optical parts such as lenses or prisms, automobile parts such as sealings or packings, or machine parts such as shock absorbers, gears or bearings.
The rubber may be a material of wiper blades of automobile windows, or tires, sealings or the like of automobiles, bicycles or the like.
Objects made of such resin or rubber may be generally used at portions causing a friction with respect to other objects coated with lubricant oil for improving a lubricity. However, the amount of lubricant and therefore the lubricity at these portions decrease with time. The method and apparatus of the invention may be used to form the carbon film, and typically the DLC. film having a good lubricity at these friction portions, whereby low friction properties can be maintained for a long time. If the method and apparatus of the invention are employed for objects made of, e.g., resin having a low heat resistance, the heat resistance can be improved.
In addition to the materials described above, ceramics may be the material of the deposition target object for carbon film deposition according to the method and apparatus of the invention.
In the case where the carbon film is formed on the deposition target object made of an organic material by the method and apparatus of the invention, such pretreatment gas supply means may be employed that can supply, as a pretreatment plasma material gas for the deposition target object, at least one kind of gas selected from a group including, e.g., a fluorine (F) -contained gas, a hydrogen gas and an oxygen (O2) gas. In this case, the carbon film is deposited on the object after exposing the object to the plasma of the pretreatment gas.
The above fluorine-contained gas may be a fluorine (F2) gas, a nitrogen trifluoride (NF3) gas, a sulfur hexafluoride (SF6) gas, a carbon tetrachloride (CF4) gas, a silicon tetrachloride (SiF4) gas, a disilicon hexafluoride (Si2F6) gas, a chlorine trifluoride (ClF3) gas, a hydrogen fluoride (HF) gas or the like.
By exposing the deposition target object to the plasma of the above gas, the surface of the object is cleaned, and the roughness of the object surface is improved. These contribute to improvement of the carbon film adherence.
When employing the plasma of the fluorine-contained gas, fluorine termination is formed at the object surface. When employing the plasma of the hydrogen gas, hydrogen termination is formed at the object surface. Since fluorine-carbon coupling and hydrogen-carbon coupling are stable, the above termination treatment can provide stable coupling of carbon atoms in the film with fluorine atoms or hydrogen atoms in the object surface portion. Owing to this fact, it is possible to improve the adherence between the object and the carbon film to be deposited subsequently. When employing the oxygen gas plasma, contaminants such as organic matters sticking onto the object surface can be particularly efficiently removed, which can improve the adherence between the object and the carbon film to be deposited later.
According to the invention, the pretreatment of the deposition target object by the plasma prior to the carbon film deposition may be performed several times with the same kind of plasma or different kinds of plasma. For example, after exposing the deposition target object to the oxygen gas plasma, it may be exposed to the fluorine-contained gas plasma or hydrogen-contained gas plasma, and then the carbon film may be deposited thereon, in which case, after the object surface is cleaned, the fluorine or hydrogen termination is formed at the object surface, so that the carbon film deposited thereafter has a very good adherence to the object.